text:
Has the flight deck access protocol changed after Germanwings 9525?
After 9/11, the flight decks were redesigned so you couldn't get in without a code, but whoever's on the flight deck could lock out everybody for 5 minutes.
A few years ago, a copilot locked out the pilot, and crashed the plane.
Since then, was the flight deck door design modified so that the pilot can always get in?
I realize this could allow a hijacker to coerce  the captain when he goes in the cabin, but that would prevent a crash.

The current flight deck door technology is explained in that answer, there is no difference between "cabin crew" and a pilot who left the flight deck in that regard. For protocols, see What is the two-person cockpit rule, as of February 2020? and What safety rule replaced the now-rescinded two-person rule (after Germanwings 9525)?

To answer directly your question, collecting information provided by @Bianfable:

The cabin access has not changed, at least officially. A crew member (commercial or flight crew member) can enter the flight deck with a code. This works well in case of pilots incapacitation.
However this possibility could be used by a criminal to coerce a flight attendant into opening the door, so there is a possibility for the flight deck crew to oppose this access each time the code is used.
Indeed a suicidal pilot could use this denial procedure to block the door. If a safety procedure existed to open the door in spite of the flight deck crew opposing it, it is obvious it wouldn't be disclosed to the public.

Instead the rule for a single person in the flight deck has changed. See What is the two-person cockpit rule, as of February 2020?. This change can prevent a suicidal pilot to crash the plane, by not allowing them to be alone in the flight deck, giving the possibility to the other crew member to open the flight deck door.


text:
What do the variable bleed valves on a CFM56 engine look like when starting said engine?
What do the variable bleed valves look like internally when starting engines? Does it exist a video of the VBV in operation?

You can see a valve opening and closing in this Youtube video:

This is frm a CFM56-5B engine, seen from the bypass duct, the primary duct is visible through the hole. A bit of explanation:

The control mechanism is actuated by the hydromechanical unit (HMU), it moves a flexible circular shaft commanding the 12 VBV. When the VBV are open, air from the primary flow is dumped into the bypass flow to prevent a compressor stall.
By the way you can also see on the picture the rings of the variable stator vanes, also part of the compressor geometry optimization at different rpm.
Picture and video taken from Why does the CF6/CFM56 Turbofan Fan Frame contain 12 circular holes between the primary and secondary flow?. This question provides additional details and explanations.

source: Stack Exchange

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sort: votes


text:
Why is a circling only approach published at this airport, Naples municipal, KAPF?
KAPF has GPS-A and GPS-B approaches, and the final approach course is exactly aligned to the runway heading.

For runway 32, GPS-A approach’s final approach course is 317°, and the runway heading is also 317°.

GPS-B approach has same heading as runway 14.

E.g. approach for RWY 14:

See also available procedures and airport diagram.
It looks normal straight in approach. But they only has circling approach on the procedure chart. Are there any valid reason for not publishing straight in?

And an educated guess is because it only has circling minimums applicable, as opposed to straight in minimums.

The answer is detailed in The Power of Paint. Just paraphrasing (here for RWY 32, but the same applies to RWY 14):
Conditions to be an instrument straight-in

There are three conditions stated in the FAA Instrument Procedures Handbook (FAA-H-8038-16B) preventing straight-in minimums:

The final approach course alignment with the runway centerline exceeds 30 degrees, which isn’t the case here.

The descent gradient is greater than 400 feet/NM from the FAF to the threshold crossing height (TCH). The actual descent gradient here is 316 feet/NM.

A runway is not clearly defined on the airfield.

The third condition is met.

Runway 32 does not have instrument-runway markings; i.e. lacks the paint to make the runway clearly defined.

Clear definition of a runway
Specifications from AC 150/5340-1M:

From Bing Maps, corresponding standard markings at Chicago O'Hare:

KAPF RWY 32 doesn't meet this standard. From Bing Maps:

The runway designator and the centerline markings are valid, but the threshold comb and the touchdown zone markings are missing. Straight-in minimums cannot be determined, only circling minimums can appear on the procedure and, since the runway is not properly identified:

Approaches that do not have straight-in landing minimums
are identified by the type of approach followed by a letter.

The perfect user to answer this question!

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text:
Where are the DC-3 parked at KOPF?
I recently learned that Florida Air Cargo operates three DC-3 from Miami Opa-Locka Executive Airport (KOPF).
Since I am flying into Opa-Locka this week, I would like to know where the DC-3 are parked, so I can handle my aircraft on the nearest ramp, shoot a photo and, if possible, walk around the ramp area to see them.

Google Maps knows where Florida Air Cargo ramp is:

Source. The DC-3 are not visible on the aerial view, but you can see them on Street View from the road NW of the ramp. DC-3 are apparently parked here, between the two west hangars, when not dispatched:

Source:
And ohoh... now the crew read your question and is waiting for you:

Source.

Joined just to say this - looks like you can see one off the NW145th St and NW 37ct, above the Sky Harbor Group: https://www.google.com/maps/place//@25.9077646,-80.2639384,244m


text:
Why are METAR issued at 53 minutes of the hour?
Why are METAR routinely issued at 53 past the hour, not at "o’clock"?

In short
H:53' is a pretty uncommon schedule, typically used for US METAR. It's an organizational choice: The weather stations, contributing to several weather reports, are fully dedicated to US METAR issuance for a period of 6 minutes each hour, from H:47:20 to H:53:20. The stations observations are then used by prediction applications issuing their own results at the top of the hour.

General case
From WMO Aerodrome Reports and Forecasts:

A METAR is issued at hourly or half-hourly intervals

Apart for the frequency, there is no precise schedule. In practical there is a variety of timings:

LFPG: Charles de Gaulle International Airport, H+00' and H+30'.
EGLL: London Heathrow Airport, H+20' and H+50'.
KLAX: Los Angeles International Airport, H+53'

Aviation weather reports are often provided by automated systems, ASOS (mostly aviation data) and AWOS (aviation and additional data). Automated reports are normally identified by the word 'AUTO' after the issuance time. In this case the period is likely constant. However WMO, the international weather organization, another UN agency working with ICAO for the weather topics, sets no general rule.
ASOS and AWOS stations typically update their observations at one- or five-minute, intervals. METAR are not updated so quickly, but results can be transmitted at this frequency using UAT (more).
US specific case at 53'
53', 54', 55' and 56' are typical of US METAR issuance time. The reason is the ASOS stations perform observations and prepare different reports but are fully dedicated to METAR from H+47:20 to H+53:20:

Starting at 47 minutes and 20 seconds past the hour, the ASOS begins to make its routine observation. By 53 minutes and 20 seconds after the hour, the observation has been prepared and edited and should be ready for transmission. Many of the hourly METARs will carry an issuance time of 53, 54, 55 or 56 minutes past the hour.

This period of time between 47:20 and 53:20 minutes after the hour is known as the “lockout period.” During this period, the ASOS is prevented from issuing any other reports, including special reports (SPECIs), no matter what weather may be occurring. The ASOS still continuously monitors and records the weather during the lockout period; it just can’t issue a surface observation

Source. This is confirmed by a NTSB report using the same wording:

The ASOS transmits an official meteorological aerodrome report (known as a METAR) at 53 minutes past each hour and a special weather observation (known as a SPECI) as conditions warrant; such conditions include a wind shift, change in visibility, and change in ceiling (cloud cover or height). The system is prevented from issuing any reports between 47:20 and 53:20 after the hour (known as the lockout period) so that the hourly
observation can be prepared, edited, and transmitted.

An ASOS at Borger, Texas:

Source.

In the US, METARs being issued at :53 (and also as needed for significant changes) is nearly universal. You may see an hourly observation at :50 or :55 or some other minute, but it’s pretty uncommon. What has driven that standard of :53 is an interesting question.

In Canada, METARs are

taken every
hour on the hour at over 200 aerodromes and other locations in
Canada.

E.g.:
METAR CYUL 280100Z 01006KT 15SM SKC 17/12 A3002 RMK SLP169=
METAR CYUL 280000Z 35003KT 15SM FEW250 17/12 A3001 RMK CI1 SLP166=
METAR CYUL 272300Z 31002KT 15SM FEW100 SCT250 18/12 A3001 RMK AC2CI2 SLP166 DENSITY ALT 500FT=
METAR CYUL 272200Z 36004KT 15SM FEW040 FEW120 FEW250 19/12 A3000 RMK SC1AC1CI1 SC TR CI TR SLP162 DENSITY ALT 600FT=
METAR CYUL 272100Z 34003KT 270V350 15SM FEW035 FEW040 FEW250 20/12 A3000 RMK CF1SC1CI1 CF TR CI TR SLP160 DENSITY ALT 700FT=
METAR CYUL 272000Z 31005KT 220V340 15SM FEW035 SCT040 SCT250 20/12 A3000 RMK CF1SC2CI1 CI TR SLP163 DENSITY ALT 700FT=
METAR CYUL 271900Z 34008KT 15SM SCT040 SCT250 20/11 A3000 RMK SC4CI1 CI TR SLP162 DENSITY ALT 700FT=

In the U.S.,

The METAR is a scheduled observation between 45 and 59 minutes past the hour.

But practice can vary.

This does not seem to answer why the METAR is issued in this time range (which was the question). It only confirms that it's normal in the US.

53 happens to be smack-dab in the middle of 45 and 00. Well - off by 30 seconds.


text:
Why does the sound of a propeller aircraft seem like the one of a jet aircraft?
Last week I saw two planes with three propellers on each side of the wing. I found it strange I could distinctly hear jets.
My first thought was they were C-130, but I haven't heard of any modern plane that runs six propellers in conjunction with jet engines.
What plane could that be? Any explanation for seeing propellers and hearing a jet sound?

It would likely be much easier to answer this if you specified your location

Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking.

All currently flying large propeller airplanes use turboprops, which are essentially jets driving turbines driving a propeller. So, seeing a propeller and hearing a jet is completely normal. (Basically, the thrust of the jet engine is not used to propel the aircraft directly, rather, it is used to drive a turbine. That turbine, in turn, drives the propeller.)
There are no six-engine turboprops currently flying, and the last six-engine large airplane was the Antonov An-225 Mriya with its six turbofans, which was unfortunately destroyed during the early days of the Russian invasion into Ukraine.
The drop tanks on the Lockheed C-130 Hercules look very similar to the engine nacelles from certain angles, and are almost evenly spaced between them, which can make them look very much like two extra engines from certain angles:

An RAAF C-130J Hercules military transport aircraft installed with external fuel tanks. Credit: © Royal Australian Air Force.
So, I would guess it is possible that you saw a C-130.

And really, a turbofan (which is what most people think of as a 'jet engine' today) is just a turboprop with the propeller stuffed inside a tube, when you get down to it...

And the CFM RISE is just a turbofan without the tube. Or an infinite-bypass turbofan, if you will.

No I could count the propellers and see them spinning three on each wing

I figured has to be Military because they were flying very close together and flying basically the exact same flight path... Training flight I assumed. I live in Minneapolis and we've got The Air National Guard airlift wing operating out of Fort Snelling which basically an extension of or adjacent to the Minneapolis International Airport

@JesselynKayMeszaros There's just not that many planes with six engines period, even if you count vintage planes.  If you only count ones with exposed props, the number is tiny. And presumably you would have noticed if you were looking at a 1930s Tupolev or some sort of flying boat, so we can reasonably exclude anything particularly old.  So that pretty much leaves the Hercules and misidentifying the external tanks (which is moderately common).

@JesselynKayMeszaros That said, if you really don't believe that ID, maybe you could edit the Q to give more details about the shape of the plane you saw -- wings high or low, engines in the wing or in pods, tail shape, etc?  Might help narrow down an ID.


text:
Why were "pattern a" and "pattern b" removed from the Instrument Flying Handbook?
If you search around on the Internet, have an older copy of the Instrument Flying Handbook, or talk to a seasoned CFII, you may run across the concept of "pattern a" and "pattern b." These were exercises which involved tracking courses, flying procedure turns, hold entries and sometimes constant speed climbs and descents. They seem like valuable maneuvers for honing instrument flying skills.
At some point in the last several years they seem to have been removed from the Instrument Flying Handbook. I don't actually own an out-of-date copy of the handbook to verify this, but if they were removed I'm wondering if anyone knows why. Does the FAA frown upon the use of these maneuvers in training?

Beyond the question itself, I'd love to find a current publication that teaches pattern a and pattern b for reference.

This pattern originated from early Instrument flight training. There were two primary training patterns ( A and B), used to build onto the basic scan. This is a primer to reference approach plates, away from the approach environment. A student would now follow these instructions in addition to aircraft control.

I can't say for sure, but I would assume that the pattern-based drills were removed because of the new emphasis on scenario-based ("real world") training the FAA has been moving toward: While Pattern A and Pattern B are useful for honing your skills (and I'll even admit they're kind of fun to fly) they're not something you'll fly in the "real world" - you are unlikely to string together that particular set of elements in that particular order on any kind of regular basis.
That doesn't mean the Pattern A / Pattern B maneuvers are not useful tools or that the FAA "frowns on" them - they really don't care how you acquire the skills necessary to pass your checkride and if flying Pattern A / Pattern B helps then by all means fly your heart out! Just know that when you take your checkride you will not be asked to "Fly Pattern B" - it's not an element of the practical test.

A copy of the maneuver diagrams for Pattern A and Pattern B can be found in Gleim's Additional Instrument Flight Maneuvers handout, which also has some valuable notes on how the maneuvers should be performed.
Personally I prefer the diagrams from Privilege Aero because I find them a little easier to read (Patterns A & B are listed as Patterns D & E respectively, except the Gleim version of Pattern B includes a descent & go-around at the end of the hold).
I've reproduced the Pattern E diagram below in case any of the links above break.

That looks absolutely nothing like an "e"!

@RalphJ To be fair it doesn't resemble an A or B either :)

@voretaq7 I'm glad you posted that diagram when you did. Is Privilege Aero down? Or did that link never work?

@ryan1618 and anyone else looking - after a lot of searching, I found the pattern diagrams matching the one posted above. Check here for the PDF.

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text:
Why is the mammatus cloud formation so dangerous?
I have read and heard that the mammatus cloud formation presents a danger to aircraft and is often associated with funnel clouds and tornadoes. How is it formed and why is it dangerous?

Source: Wikipedia

Would probably get better answers in Earth Science.

I want aviation-specific answers so I disagree. Thanks for the comment though.

Anedoctal: The only two times I has seen this cloud formation was the only two times I witnessed tornados forming. Also try to find a video, the strong winds gives that clouds a terrifyng "burbling". I'm pretty sure no one wish to go straight or under it

Nobody knows exactly how mammatus clouds are formed, it's been studied and there are several theories about it but none are accepted. They are most often seen below anvil clouds, ie cumulonimbus clouds with extremely powerful updrafts. One thing that the theories all agree on is that where they are formed on the underside of cumulonimbus clouds there are huge shifts in temperature, moisture and pressure within a short space of time. Although these clouds can form under other types of cloud they are mostly seen under the most powerful of storms.
So why are they dangerous?

They are usually made of ice: ice accretion is dangerous, especially for light aircraft without de-icing systems
They are almost always associated with severe low level wind shear. Wind shear is sudden changes in wind direction which is dangerous for aircraft. You can suddenly find that a 30kt headwind is a 30kt tailwind so you've lost 60kt of airspeed, this is especially dangerous during takeoff and landing
They are almost always associated with severe convective activity, ie very strong updrafts and downdrafts which are dangerous for aircraft. You could get sucked up thousands of feet or pushed down as well, and there's be nothing you could do about it
They are almost always associated with severe turbulence which is also dangerous for aircraft. Severe turbulence is at best extremely uncomfortable, at worst can cause a loss of structural integrity

So mammatus clouds are usually an excellent sign of an area to be avoided.

I was in a turboprop approaching Antigua for a honeymoon with my wife (we were passengers not pilot). And while I've experienced turbulence before had never been exposed to a downdraft. It was terrifying, we dropped a good 20 feet in the space of three seconds. And from that day on, I've made certain to keep my seatbelt buckled while in my seat (I actually lifted out of my seat during the drop.)

Maybe he meant 200 feet. 20 feet's nothing.

You offer several assertions here, all without citation, several of which are questionable, and at least one of which is definitely false: these cloud formations are generally not made of ice, as they are generally a low altitude, warm weather phenomenon. Their association with severe weather is true, but not directly. These exact formations themselves may be benign, though found in the vicinity of severe weather.

Mammatus clouds are very gentle downdrafts, typically seen beneath the anvil or along the flanks of a thunderstorm, though they may also be occasionally seen under stratus and altostratus clouds. The reason for the udder-like shape is not well understood, though there are several interesting theories. Aircraft flights through the udders has described them as "rain-filled sacks" with very light turbulence. They are not a sign of heavly turbulence or severe weather, though they are often found in the aftermath of a severe thunderstorm (or any thunderstorm). Their most distinctive characteristic is their attractive appearance.

Based on the fact that mammatus clouds are associated with crazy air currents, it would very easily throw an airplane out of control.

This doesn't really answer the question.

It says the same thing as the newer answer, just without any details.

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text:
How to trigger warnings on an unplugged aural warning unit?
I got an old 80-0557-11 Rev A manufactured by Grimmes from an EMB-120 Brasilia, and I was wondering how to make it speak.
I powered the component with a 28VDC power supply. It only said "Aural unit Ok" while I was expecting a lot of warnings, due the lack of connected sensors.
Checking an old wiring manual, I realized that most of the sensor inputs have a single connection, not a "HI/LO (+/-)" lines.
Does someone have some idea about how make it play alarms?
Thank you in advance for anyone who can explain me the logic of the system. Please, keep in mind that I'm just a enthusiast trying to better understand how this system works.

I suspect that "Aural Unit OK" is just an internal self-test. In order for it to "speak what she knows", it may have to be hooked into real (or simulated) signals. Without having a wiring diagram or information on how this unit hooks up and communicates, it will be a very difficult question to answer. While not off-topic because it requires product-specific information, this knowledge is highly specialized and it may be unlikely to get an answer here.

@RonBeyer Thank You for your comment Ron, i understand that's highly speciacialized knowledge, but maybe it's not a mistery like we expect. That's the reason why i brought this question to this room! :)

Are you sure it should say something when powered on but without the various sensors? It may be working exactly as designed. Sounds like you've got (at least some of) the manuals, so that, mostly likely, makes you more expert on this than any of us. (Unless, of course, an A&P happens to wander by who knows this particular unit...)

This Ops Manual may be of help.  The aural unit can pass-through audio from devices such as the TAWS or TCAS. Most of the other alerts are internally stored audio files that are triggered by the external systems. The single wire connections are discretes.  They may be OPEN/GROUND (try grounding to see if it triggers) or 28V/OPEN (applying 28V will trigger).

@Gerry The Ops Manual tip was great. I was analyzing just the aircraft maintenance manual. I'll try to grounding and if it doesn't work i'll look for more info if it's safe to apply 28V on this lines. Thank you Gerry! :)

I used to fly this plane, "aural unit ok" is indeed what it says when you first power up and it completes it's self test.  You will probably need to hook up an alarm cancel button, IIRC at first power up a lot of the warning circuits are lit up but it doesn't say anything until you cancel an alarm, the trigger goes away, then comes back.  Also, a lot of the warnings are inhibited with weight on wheels so you may have to simulate that signal also. Good luck, I want to hear some recordings when you figure it out!

Thank You Guys! Because you all i accomplished to make it work! :) @nexus_2006 please, send me your email by private message, i'll be glad to share with you!

@drmwndr Stack Exchange doesn't have private messaging, but if you look at my profile you can see my github name nexus2006 and in my profile there is a public email, thanks!

Answering my own question based on tips posted on comments:
As @Gerry suggested on comments, they are OPEN/GROUND, if i ground any of sensor cables it'll trigger the alarms. Those lines are 5V, and i think that most of sensors are just simple switches, except for the Fire Alarms, that i  couldn't trigger and has 6.8V over its line.
For now i got my AWU speaking.
Thank everybody who commented with their suggestions. Those were very very very useful,  you guys are awesome!

The fire signals come from something called a 'fire loop', which is basically a wire-shaped thermistor wrapped around the engine/apu.  Maybe researching that will lead you to a solution.  Its amazing you didn't fry your box experimenting with it, good work!


text:
Does tailless means no tail at all?
When I was reading about the HAL Tejas I observed that it was described as a "tailless" plane. However I could see a tail in the picture.
After careful reading I am assuming that being tailless means not having any tail planes a.k.a horizontal stabilizers.
Does tailless means no tail at all?

It seems there are two questions: 1) Does tailless mean no tail; and 2) Are delta winged planes tailless. Please disambiguate.

No, not at all - there are at least two Delta Wing aircraft that feature a conventional tail, and they are the Gloster Javelin and the Mig 21
https://en.wikipedia.org/wiki/Gloster_Javelin

https://en.wikipedia.org/wiki/Mikoyan-Gurevich_MiG-21

(Courtesy of http://airheadsfly.com/)
In addition (and I believe this is within the spirit of what you've asked) you then you have aircraft such as the Eurofighter Typhoon or Saab 37 Viggen which feature canards:
https://en.wikipedia.org/wiki/Eurofighter_Typhoon

https://en.wikipedia.org/wiki/Saab_37_Viggen

Ultimately, "Delta" only describes the wing shape - though there of course features of the shape that will lead to many designs appearing similar. The Wikipedia article has a nice infographic showing the general variations of Delta Winged designs:
https://en.wikipedia.org/wiki/Delta_wing

Since the MiG-21 is using a general TsAGI-developed configuration, there are several Russian aircraft from that era which use a tailed delta, such as the Su-15 or the M-50

Tailless means no horizontal tail, but a vertical tail is still allowed. Examples are the Convair F-102 or Convair B-58.

Convair B-58 Hustler (picture source)
Compare this to a flying wing: Here even the vertical tail is left off. Since a classic delta would have too little lever arm for yaw control, this requires a higher aspect ratio wing. An example is the Horten IX:

Horten IX V1 prototype aircraft (picture source)

You might want to add the B-2 because it is the extreme example of no vertical and horizontal stabilizers.

@SMSvonderTann I'm not aeroalias. One picture per point should be enough, and the Horten is the better-looking of the two ;-).

Tailless usually means no horizontal stabilizer (tailplane). Until the postwar era it often also included planes with no tailplane but instead a "canard" foreplane in front of the wing, however we nowadays recognise the canard and tailless configurations as distinct, some even talk of the canard as "putting the tail in front of the wing". One or two experimental types without a vertical tail fin have also been referred to publicly as "tailless" but this is technically incorrect.


text:
Does the Boeing B787 have safety issues with its battery and windshield?
AVHerald has reported

An incident of battery overheating. That is after the aircraft has been grounded and parts of the battery system redesigned. AVHerald provides a detailed report on the battery issue.
An incident of a cracked windshield. A cracked windshield typically results in declaring an emergency. AVHerald lists 15 incidents of cracked windshields since 2012. This happens in other aircraft too, but apparently not in the same way. On other aircraft, only the outer of several layers cracks after some time. On the 787 it seems to happen on start or landing, always resulting in a return to the airport. It should be noted, that the 787 windows have fewer layers and larger windows than any other type.

Also Forbes reports, that there have been at least four incidents with the batteries after the FAA mandated four-month grounding, and a physics professor at Canada's Dalhousie University states battery failures are an indication of a problem within the cells.
Incidents with both issues have been reported since 2013, when the 787 was allowed back into service after the FAA mandated four-month grounding.
To me reading this report is disturbing.

Doesn't this mean, that the aircraft is flown with knowingly unsafe battery and windshield?
As a passenger, does one have to be worried about flying in this particular type?

Comments are not for extended discussion; this conversation has been moved to chat.

The 787 is among the safest airliners currently flying. At the time of writing, it has been involved in zero hull loss incidents and there have been zero fatalities due to incidents.
While you can find numerous incidents including those you mention there have been exactly zero total losses and no loss of life on board (due to the aircraft itself - its possible people may have perished on board due to other factors not involved in aircraft safety).
It should be noted that A boeing report on this subject points out (page 19) that most of the aircraft which have had zero hull losses have also not accumulated 1 million departures. Therefore it might be too early to tell if there is any fundamental safety issues with these types. However, there has been 50+ years of learning about safety with regard to aircraft operations - and all of that feeds in to these modern aircraft.
All in, I would consider flying on the B787 to be objectively safe (or, at very least equally so as other similar airliners). Does there exist some "wrinkles" to be ironed out? Perhaps - but they do not affect the overall safety of this type.

There’s an old saying that in the industry that just because there are no accidents does not mean that it safe.

Although a highly voted answer it's a bit dangerous. Concorde had 0 haul-losses until one of them was lost. And that was the end. Also you need to take into account the number of units built, the total hours flown by all of them, the total miles flown by all of them etc. I don't know if the Boeing research takes that into account don't have time to read. But if it does, it might be better to add some of them, as links (especially from big companies) tend to be extremely fragile...

@SteliosAdamantidis The concorde accident was not the end - it was the changing economical climate which was the end. It had nothing to do with safety - again, the safety problem which occurred was fixed and retrofitted.

@Jamiec From Wikipedia On 10 April 2003, Air France and British Airways simultaneously announced that they would retire Concorde later that year. They cited low passenger numbers following the 25 July 2000 crash, the slump in air travel following the September 11 attacks, and rising maintenance costs. Anyway I don't want to stick to Concorde. I consider the rest of my comment more important.

The comments to the question were moved to chat. The most interesting part: https://youtu.be/UqIzcuNpXP0 It's a documentary that shows, how FAA regulators who are "nice" to Boeing get cushy jobs at Boeing afterwards, and how people who pointed to the problems are now ruined...

@mike now you're getting in to conspiracy theory territory. I'm not going to comment on that.

@Jamiec Just watch the documentary. The guy they are talking about really  worked for the FAA, now he really works for Boeing, go figure...

@mike Im sorry, I dont have the time for a 52 minute youtube right now :)


text:
What types of gear/supplies are "must-haves" for private pilots?
Is there certain gear that people consider "must-haves" for a private pilot? Specifically, a new pilot or student pilot.

I'm voting to close this as it is opinion based.

@GdD I would say that it could become opinion based but also could go the other way and have some general answers.  It wouldn't be hard to say something like "Access to an airplane" as a must-have for example.

Taking that logic it becomes too broad @dalearn. Access to an airplane, money, limbs, half a brain are all essentials.

@GdD Yes, it can become too broad but it doesn't have too and easily could turn out to end up with several common-sense answers that are not too broad in scope.

Flight bag.
Sectional for the area to be flown in.
Headsets usually, to protect hearing, if not to hear ATC better.
POH if not in the plane already.
Kneepad for taking notes, something to write with.
Water.
That's a bare minimum list, for a casual flight in a known area.

Wouldn't say most of those were must-haves.  I've never owned a flight bag, for instance.  (And got my PPL in the '70s.)  Headphones if you're renting, and the rentals don't come with them; otherwise they're part of the airplane.

For casual flying in a known area, assuming uncontrolled (class G) airspace, so far I haven't needed to write anything down in-flight. I agree that a way to make notes in-flight can be beneficial if you're flying under, or potentially under, ATC control.

Sunglasses might also be useful.

Get a good headset and a decent mobile device that can run a charting app. I use my Moto4 with Avare.
Download The Airplane Flying Handbook -and- The Pilot's Handbook of Aeronautical Knowledge from the FAA site (both free).  Also download the Airman Certification Standards (ACS) for private pilot airplane.
The only books that I usually recommend people actually purchase are the aircraft manual and a written test study guide from ASA, Jeppesen, Gleim, or King.


text:
How realistic was the airplane scene in Terminator Dark Fate?
In the movie Terminator Dark Fate, the C-5 Galaxy Grace (Mackenzie Davis) is flying gets hit by another plane (I think it's a KC-10 Extender) piloted by the Rev-9 Terminator.
What I want to know is how realistic (or not realistic) is this scene. Wouldn't wake turbulence cause an issue?
Part 1 of the scene:

Part 2:

I was hoping you would ask about the Boeing 747 crash scene, which was amazing.

Completely and utterly ridiculous. Let me count the ways:
First video:
0:22 That collision would have destroyed the bigger plane as well, rendering the entire rest of the scene impossible.
0:35 As you mentioned, the wake turbulence would have knocked the trailing airplane down and away.
0:46 There's no way that collision lasted for that amount of time.
1:11 The autopilot would not have been able to function with that level of damage. It wouldn't have even attempted to activate.
1:19 The front of the plane isn't damaged, so the only wind would be from eddies from the hole in back. Which would be pretty strong, don't get me wrong, but not nearly strong enough to pick up a full-grown woman.
1:33 Gravity doesn't just "go away" when you lose two engines. Not to mention the wind described earlier would still be a factor.
Second video:
1:22 Having one parachute open would have slowed the fall of the Humvee quite a bit. It wouldn't still be in freefall.
Note that I'm only covering the aviation-related ridiculousnesses in that scene. There are quite a few other ways it fails basic physics as well.


text:
What is the ATFM Project BOBCAT and why is it important?
Aerothai, the ANSP of Thailand, runs an ATFM Project called BOBCAT (Bay of Bengal Cooperative Air Traffic Flow Management System).
Why is it so important? And why is an ASNP from Thailand running a project, that spans across most of South Asia?

@Federico I'm not sure of the relevance of the Meta thread you linked. In particular (related to your answer there), this is not a question from a new user: it's from somebody who's been here for three years. Also, "This question does not show any research effort" is given as a reason for downvoting on the mouse-over text of the downvote button, so is clearly something that's discouraged across the whole network.

This looks like the sort of question where you can at least find out the basics with Google. Please do so, as people tend to be disinclined to put effort into answering a question whose asker also seems to have put in no effort.

@DavidRicherby Did I not clarify the question in the meantime? I'd like to know, why this is so important, ANSPs in the region seem to refer to this and I want to know why. When you google the project, you find a little information, but not why this exists and why aerothai does this. I'd also like to clarify, that I don't come here, so that other people google an answer for me; I come here knowing, that this is an aviation community, so I thought, people involved or people in the know would be able to answer.

No, you clarified it nearly half an hour after my most recent comment.

@mins Important to other ANSPs in the region

Not sure Aerothai is an ANSP, seems more like Arinc. See also. BOBCAT seems to be the equivalent of CFMU (now NMOC).


text:
What is the current status of the deployment of RNP 1 and RNP 2 airspaces and approaches in Europe?
Is there an overview of the deployment of RNP 1 and RNP 2 airspaces and approaches in Europe?
I'm looking for a map, that shows this information. Maybe even 'special' solutions that are not quite RNP.

A few years ago, each country in Europe had its own authority and plan for air traffic management. But this little continent is today the most busy in regard to air traffic, and without action, growth is nearly impossible. Thus countries have agreed to build a "single sky" system, the initiative is known as SESAR (here is the master plan). Those actions are part of the "Pilot Common Project" (PCP), sub-projects include "ATM functionalities 1" (AF 1). From the master plan:

Enhanced terminal airspace using RNP-based operations consists of the
  implementation of environmentally friendly procedures for
  arrival/departure and approach using PBN in high-density TMAs, e.g.
  RNP 1 standard instrument departures and arrivals (RNP 1 SIDs and
  STARs).

and:

Enhanced terminal airspace using RNP-based operations with RNP 1 SIDs,
  STARs and transitions (using radius to a fix-RF) and RNP APCH (lateral
  navigation/vertical navigation (LNAV/VNAV)) is planned for
  synchronised deployment at the 24 busiest airports in Europe by 1
  January 2024

The schedule:

The current implementation status for the 24 airports selected (from SESAR monitoring view):

While initially planned for 2018, RNP operational use is now planned for January 2024. Out of the 24 high density TMA (equivalent of FAA TCA), two are already ready (and RNP 1 is already operational for helicopter low routes in Oslo -- this early use is likely for environmental reasons).

I made this question a community question, it is open to improvement by anyone.


text:
Can a US airline add an employee passenger as crew?
Suppose an airliner flight is full with passengers and the airline staff realize afterwards that there are employees who the airline wants to send to their shifts using that flight.
The airline staff decides to ask for volunteers to surrender their seats in exchange for compensation, but they don't get enough volunteers to make room in passenger seats for their employees to take.
Would it be legal for the airline to instead have one or more of the employee-passengers take the flight as "extra crew" (assuming there is an extra seat to strap into in the crew areas)?

First of all it depends on what type of "employee" and if the jumpseat is in the cockpit or the cabin.
According to the answers to this question there are no regulations on who may sit in a cabin jumpseat as long as it meets the specifications set out in FAR § 121.211 for proper airline seats. So the airline is free to set policy for cabin jumpseats.
As for jumpseats on the flight deck the restrictions are quite stringent. If the employee is a pilot FAR § 121.547(c)(3) allows off-duty pilots to fly in a jumpseat on the flight deck, so there would be no need to make them an active crew member.
FAR § 121.547(a)(1) allows an on-duty flight attendant to fly in a jumpseat on the flight deck. The person would have to be a certified flight attendant, so you couldn't just make any employee a crew member. Remember also that flight attendants have hours of service restrictions, so any time they are considered on-duty has to comply with the h.o.s. regulations.
Certain other types of employees are allowed to fly in the flight deck, but they have to be performing a specific function on the flight that requires their presence in th cockpit. For example, a mechanic could fly in the cockpit if he's there to monitor something on the aircraft. A flight dispatcher could be on the flight deck if they are observing flight operations as a part of training.
Even some persons who may be given access to the cockpit for operational need, like air marshals or training personnel, still must have a seat available in the cabin.
So they can't put someone in the cockpit just to transport them from place to place and they couldn't just plop a salesman or a ticket agent there and say they are a "crew member."
There are regulations stipulating the minimum number of flight attendants on a flight but not a maximum number. So, technically they could make a flight attendant part of the crew, but if that person was just listed as a crew member and wasn't actually performing any duties, the FAA would certainly interpret that as a violation.

Thanks! So, if they had a spare cabin jumpseat, they could have an employee use it without being considered working or crew, yes?

Yes. Afaik there are no regulations on cabin jumpseats. For pilots and FA's they still have to keep track of their hours of service because I don't believe dead-heading counts toward their required rest period

I used to work for AA and travelled as an employee quite often. The concept of involuntary bumping from a flight has been around for a long, long time, and it only takes simple arithmetic to figure out that if a flight somewhere further along the line cannot depart for lack of crew, to use one possible example, it is much cheaper to bump a paying pax, compensate according to the rules and get the employee where he/she needs to be, than cancel the flight that employee needs to be on. Employees dead-heading to a destination for work are not considered crew by the FAA. The only way to guarantee a seat on an aircraft is to own it, and even then it's not always a sure thing. :)

With few exceptions, only pilots and flight attendants can ride in a jumpseat.  Pilots can ride in the flight deck jumpseat, and flight attendants can ride in a jumpseat in the cabin.
Other types of airline employees are not permitted to ride in a jumpseat.
It is my understanding that, contractually speaking, it is up to the employee to decide whether they want to ride in a jumpseat to their destination instead of in a regular seat.
There are exceptions in emergency situations where the pilot can, for safety reasons, decide to allow non-flight crew to sit in a jumpseat.

Airline dispatchers are also in CASS and can ride in the cockpit jumpseats. In fact, they are required to for 5 hours annually to maintain currency, but they have access to the jumpseat for leisure/stand-by travel (just like pilots) when the aircraft is booked full.

And this rule only applies to pax aircraft, not cargo.

I have first hand knowledge of mechanics riding in the jumpseat on US 121 carriers.  Also FAA inspectors will make observational and evaluative jumpseat rides.  Furthermore, there are provisions for air traffic controllers to have jumpseat rides for familiarization purposes.


text:
May a helicopter fly at night with only strobe lights?
I thought that all aircraft flying at night needed red/green/white position lights and red/white anti collision flashing beacons.
I observed a helicopter flying over houses with only its strobe lights. Is that allowed?

Is it possible you couldn't see the navigation lights?

In what country did this occur?

Welcome to aviation.SE! For questions about regulations or laws, please always tell us which country or regulator you're asking about. If your question is about the US, for example, we have an faa-regulations tag that you can add to your question.

In the US FAR §91.209   Aircraft lights. applies

No person may:
(a) During the period from sunset to sunrise… (1) Operate an aircraft
unless it has lighted position lights;
…
(b) Operate an aircraft that is equipped with an anticollision light
system, unless it has lighted anticollision lights.

There are no exceptions. A couple of thoughts though. It can be pretty dark on the ground and still not be after sunset. I live in the shadow of a mountain and the sun goes down at my house 15 minutes before sunset.
It is possible that they just forgot. Most pilots who have strobes turn them on all the time (an exception would be in clouds or fog) so they would be on.
It is also possible that they were on, but because of the position of the helicopter, you just didn’t see them.
The beacon (referred to in the FAR as anti-collision light system) does not have to be just red. Lots of them are red in back and white in front, so you may have seen just the forward facing light.
This StackExchange Post has more details on lighting.

Although not really an "exception", para B does allow for aircraft that are simply not equipped with a beacon. Although I'm sure that's not the case here.

@Jimmy I was thinking more along the lines of no exceptions for different categories of aircraft. Lots of the regs exempt helicopters or have different minimums for them, e.g. Special VFR at night doesn’t require a helicopter to be IFR equipped; Night VFR minimums are different for helicopters; IFR takeoff  minimums are different.

Ha! Yeah, after 30 years of acquiring fixed-wing knowledge, I recently started working for a helicopter company.  It took quite a while to "re-learn" all of the regs that were different for these "flappy wing" beasts.  Prior to this gig, I didn't really know a thing about them.

@Jimmy I just got my AGI and had to learn all of the regs for balloons, ultralights, helicopters, etc. Seems like everything is an exception when compared to fixed wing.


text:
What improvements did Airbus make as a result of the Air France 447 accident?
As far as I can tell, the following factors all contributed to this crash:

Pitot tubes susceptible to ice crystal blockage
Crew not aware that they can stall the airplane due to alternate law
No return to normal law after reliable speed information was available to the flight computers
"Unlinked" sidesticks which allow the pilots to command different inputs, unaware of what the other pilot is commanding
Stall warning goes quiet when the airspeed is too low

Of these, the first factor (pitot tubes) was already in the process of being mitigated. What about the other factors though? Were the onboard systems modified in any way to fix these shortfalls?
I'm no expert but it seems like at the very least that the following would help:

If the stall warning didn't stop, but instead changed into an even more ominous "you're now tumbling down at less than 60 KIAS" warning.
Also, given how extremely rare alternate law appears to be, it might not be out of order for the airplane to announce that it is now very much possible to stall the plane by pulling up (in actual words).
Finally, it sounds like the unlinked nature of the sidesticks was a big part of the problem; are there good reasons to leave them unlinked in future designs?

Some context:

Wikipedia article about the crash
CVR transcript and comments

I don't have a reference, but I remember hearing that they did fix the inhibition of the stall warning below 60KIAS.  They also now require high altitude stall awareness training for all flight crews, which should help as well.  As you pointed out, the pitot tubes were already in the process of being fixed, and they accelerated the schedule of replacements, and I believe that they have all been replaced.

Airbus should definitely implement the "You're now tumbling down at less than 60 KIAS" warning. In exactly those words.

What improvements did Airbus make as a result of the Air France 447 accident?

The official report has a section headed

5 - CHANGES MADE FOLLOWING THE ACCIDENT
...
5.2 Airbus
Review of the “Unreliable speed indication” procedure
Flight Operations Telex (FOT) of 9 September 2009 recommending, at the next recurrent
training course, a session on the simulator at high altitude in normal and alternate law
including:

Manual aeroplane handling,
Carrying out the UNRELIABLE SPEED INDICATION / ADR CHECK PROC procedure.

Most of the changes were carried out by other parties, Air France, EASA, etc.

If the stall warning didn't stop, but instead changed into an even more ominous "you're now tumbling down at less than 60 KIAS" warning.

Opinion: If the computers have decided they don't know what the heck is happening, it's probably a bad idea for them to make something up at random to shout at the crew. If the computers always know best, they should just probably shut-up, activate the cockpit wrist-restraints and fly the plane.

it might not be out of order for the airplane to announce that it is now very much possible to stall the plane by pulling up (in actual words).

Wild guess: Maybe this would help but not when the PF is already ignoring stall warnings and determinedly pulling up almost continuously. Generally less is more when the crew are likely to be confused and overwhelmed. There's probably a hundred things you can more easily accidentally do when you are flying in alternate law and when you are in alternate law you may not have time to patiently wait and listen whilst the computers enumerate them all to you.

the unlinked nature of the sidesticks was a big part of the problem; are there good reasons to leave them unlinked in future designs?

So that the pilots can engage in wrestling matches? Yes, it seems there needs to be an even clearer indication of conflicting inputs but I'm not sure if mechanical feedback is necessarily the best method. Pilots are already supposed to be trained and tested on clear handover of control.
Addendum:
Linking controls can also cause problems. This was experienced in a Boeing 777 in an incident in Air France flight 011 in April 2022. The pilots thought they had flight control malfunctions but were simply pushing against one another's inputs. Dual input events occur as often in Boeing aircraft as in Airbus aircraft despite linked controls. The AF 011 icident shows that linkage doesn't always make pilots realise that they are making opposing inputs.

Right, improved flight crew training is the answer!

Good reference, I think that answers my question exactly. Though, between "engage in wrestling matches" and "have no idea that the other pilot is pulling up", option #1 doesn't sound that silly. Gulfstream decided to implement the wrestling option, sounds like it's a matter of time now. As for the stall warning I agree if the computer decided it doesn't know, but once all the pitot tubes are back in agreement, it doesn't seem too much out of order.

@romkyns: You make some good points. I'm sure many of us mulled over similar thoughts when reading the reports of what happened on AF447. I wonder if the emphasis with the automation is that the computers should voluntarily give up control to pilots but shouldn't snatch it back unless and until the pilots agree circumstances are right for this. Maybe re-application of flight protections also comes under this principle?

In this incident, the stall warning didn't stop because the computers didn't know what was happening. Indeed, by the time that the airplane stalled, the systems were all working perfectly, with three reliable and matching airspeed indications. The stall warning stopped only because it was inhibited (programmed) to stop below 60 KIAS.  This was done with the intention of preventing erroneous stall warning indications while on the ground (and surely if the airplane is below 60 KIAS it is on the ground).  This stopping is part of what caused the confusion in the cockpit.

When control transfers to alternate law where all is this indicated? Is there prominent visual + aural indication of this quite an important transition but one which rarely happens?

@curious cat: It is indicated on the PFD and in ECAM messages. There is an audio warning.

We had one of the first A320 simulators with cockpit 1.7 standard in 2011. That had a direct Angle Of Attack tape that could be displayed on the captains' left side, as I understood that was an improvement made due to AF 447.
Update
It turns out to be the Back Up Speed Scale (BUSS), which shows red, amber and green zones, and is based on Angle-Of-Attack information. The needle needs to be kept in the green zone by providing pitch stick inputs. Flight control law is direct law.
Source: Airbus FCTM.

can you please provide sources? otherwise you shoiuld have left a comment.

Sources of what? The Airbus head of training was at hte facility and asked to check if the direct AoA tape was installed, and it was.

sources of "I understood that was..." so far this is just a personal anecdote.


text:
What are these "holes" in the F-104 for?
In this video there are two "holes" that I'm curious about.
One is rectangular in the all white section of the plane that flutters open/close during flight. The other is somewhat oval and is on the line between the blue and white areas.

It appears to slowly close with none of the "flutter" displayed by the other.

The second "hole" I am referring to is just forward of the first one, above the wing.  It is visible, for example, at 7 seconds.

Ok, I found online the maintenance manual
From part 1, page 2-233 (270 of the pdf) we find that the "holes" are the Engine Ground Cooling Doors:

Note: the nose of the aircraft is on the left in this diagram.
Furthermore, form this cutaway:

we see that the oil coolers (40 in the diagram) are behind the rectangular "hole"

Nice find, also mentioned in the F-104D flight manual: cooling air for engine ground operations is supplied through four single and four double inboard opening suck-in doors (spring loaded to closed) just aft of the firewall. It seems these doors were first added for the 1958 altitude record.


text:
How wide should taxiways be to serve a A350?
I'm planning a model airport and I really don't know how far the wing should be from the gate safety line (I think that's what it is called).
The largest wingspan will be that of an A350.

Have you looked for the airport planning docs for an A350? I've seen info like that for a variety of aircraft (A350 may or may not be included) posted here. Maybe search this site for them - it might already be available, or may point you to where you might find them publicly available.

Have you gone to "satellite view" in your favorite online map and measured a few actual airports? There's usually a scale one can use. One online map (that I know of) even has a measurement tool built right into it.

In short
Serving A350-900 with a wingspan of 64.75m, requires a taxiway with a reference letter E, which is appropriate for aircraft as large as 65m. Minimums:

Taxiway centerline distance to apron objects: 43m.

Taxiway paved area: 23m.

Taxiway paved area + shoulders: 44m.

Taxiway strip: 95m.

The recommended taxiway widths are found in ICAO Aerodrome Design Manual - Part 2 - Doc 9157.
Definitions from Doc 9157

Shoulder: A shoulder is an area adjacent to the edge of a full strength paved surface so prepared as to provide a transition between the full strength pavement and the adjacent surface. The main purpose of the provision of a taxiway shoulder is: to prevent jet engines that overhang the edge of a taxiway from ingesting stones or other objects that might damage the engine; to prevent erosion of the area adjacent to the taxiway; and to provide a surface for the occasional passage of aircraft wheels.

Strip: The taxiway strip should provide an area clear of objects which may endanger taxiing aeroplanes. Consideration will have to be given to the location and design of drains on a taxiway strip to prevent damage to an aircraft accidentally running off a taxiway.

Taxiway width
The taxiway strip width required depends on the reference letter (category) of the facility. The letter indicates which aircraft can be served. The category is based on the maximum wingspan and the maximum main gear wheel span. Table 1.2:
$
\begin{array}{c r r}
\text{Letter} & \text{Wingspan} & \text{Wheel span} \\
\text{A} & \text{15m} & \text{4.5m} \\
\text{B} & \text{24m} & \text{6m} \\
\text{C} & \text{36m} & \text{9m} \\
\text{D} & \text{52m} & \text{14m} \\
\text{E} & \text{65m} & \text{14m} \\
\text{F} & \text{80m} & \text{16m} \\
\end{array}
$
The A350-900 has a wingspan of 64.75m and a wheel span of 12.87m (see airport planning manual). It requires a facility of category E.
In your case, the taxiway would be an apron taxiway. From Doc 9157:

1.1.9 The requirements for apron taxiways regarding strip width, separation distances, etc., are the same as for any other type of taxiway.

Table 1.1 gives the taxiway width for each category of facility. The taxiway width includes the pavement and the shoulders.
For a facility with reference letter E, the width of the taxiways, including the shoulders, is 44m. Other dimensions are also provided in table 1.1.
Centerline distance to objects
For apron taxiways, an increment, denoted Z in table 1.1, is added for the separation between the wing and objects, to allow for pilot error when following the centerline. This increment Z determines the location of the taxiway centerline relatively to the object:

For a category E, this is 10.5m. It means the centerline will be distant of $\small 65/2+10.5=43$m from apron obstacles.
The same document also describes how taxiway curves should be designed, how taxiways should intersect and the minimum distance they should be separated by.


text:
How do jet engines work?
I was doing research about jet engines, and they seem really difficult to fully understand. So, can anyone explain it in a simple way?

An afterburner glows on an F-15 Eagle engine, source: Wikimedia.
How do jet engines work?

I gotta say, that engine doesn't seem to be terribly well tethered. I guess those two longer guy wires and the short turnbuckle (per side) are sturdier than they look.

Compare with http://physics.stackexchange.com/questions/114280/why-do-turbine-engines-work

In the simplest of terms:

Suck - Air is sucked into the turbine. For efficiency reasons, most aircraft let some of that just pass through the outer part of the fan, rather than through the whole engine.
Squeeze - The compressor squeezes that air together to a high pressure. This helps with ignition.
Boom - Fuel is injected and ignited. As the air gets hot, it expands.
Blow - The hot air drives the low-pressure turbine (driving the whole shaft holding the engine together), sucking new air in, and is itself blown out the back.

There's a great interactive animated GIF at NASA's K-12 page on jet engines.

if some of the air bypasses the engine it is called a turbofan engine. but that is semantics

the "suck" part is in effect only at startup/on ground. During cruise is the motion of the aircraft w.r.t. the air that makes the air enter the engine. The fan effectively pushes the air towards the back.

@ratchetfreak I'd always heard that a "low-bypass" jet engine was still a turbojet and not a turbofan, but other definitions refute that. Some specialized engines, like those for the SR-71, had variable bypass; they were technically turbojets up to Mach 2, then the bypasses were opened and air flowed directly to the afterburners.

@Federico - The "suck" part is always in effect; turbofan engines are highly efficient in part because the get engine drives a larger compressor blade that moves air around the turbojet core, increasing thrust. If that mechanism didn't work at speed, there'd be no point in having it.

@KeithS Federico is right, engines only "suck" in air when they are at no or very low speed. I think Federico was not commenting on the fact that in order to suck in air the pressure in the inlet has to be lower than the ambient pressure. This means there is a pressure gradient from high ambient pressure to low static pressure in the intake. During cruise flight this is not the case anymore, then the ambient static pressure gradient reverses.

If you understand the function of a standard 4 cycle internal combustion piston engine it becomes a little easier.  The way I have heard it explained is that in a piston engine the 4 cycles occur in the same place, but at different times.  However, in a turbine engine the same 4 cycles are occurring simultaneously, but in different places.

Users reaching this question: How does a jet engine work? (explanation for non-aviation related people) are now redirected here. This illustrative answer is in the spirit of the initial question, easy to read for a non-aviation person without sacrificing accuracy.
To create a reaction, throw something
The physical principle at work has been studied by Isaac Newton and is known as principle of reaction (or the more mouthful Newton's third law of motion).
The reaction movement is the response to another movement. In many cases, including the jet engine, this is done by moving something heavy, at the highest possible velocity.
While reaction seems magical, it's something experienced non-stop in everyday life, without giving attention to it. We can easily imagine the result of such experience:

Get a small boat and a well-sized rock, say 20 kg.
The boat is initially stationary on the water.
Throw the rock violently behind the boat.

(Legal disclaimer: Don't try this at home, I conducted this experiment a long time ago with trained personnel)
As soon as the stone gets speed rearwards, the boat gets speed forwards.
Both objects stop accelerating when the rock has left the hands of the thrower.

A note here about the velocity:

In the boat experiment, if we want to throw the rock without moving the boat, instinctively we'll move it very very slowly until it is above water, then let it drop into the water without pushing, and it'll work.

We also know what happens when a big gun throw a 500 g shell at the speed of sound: There is a huge reaction of the gun, in spite the gun is heavier than our boat and friction on the ground should prevent it to move.

Feel reaction intuitively:
When we push on the rock, we are actually using the rock as a fulcrum, and creating the reaction this way, we push on the rock, we move the boat. However to continue generating thrust, we need to push on the rock stronger and stronger, because the rock itself is accelerating due to the force we apply to it. If we just move our hands at the speed of the rock, we are not pushing, the motion of the rock is unchanged due to second law of motion, there is no impulse, thus no change in momentum, and the boat just starts being slowed down due to drag (from water), and the rock too (drag from air).
Actually the force effects we create by pushing (accelerating) the rock are split between the rock and the boat according to the ratio of the masses. The largest mass gets the smallest change.
Reaction from throwing air
Throwing stones is obviously not practical for an engine. But we can throw air, like in a balloon, again something very familiar:

This principle of ejecting air to create a reaction has been known since Antiquity with the aeolipile. It was an early steam engine. Air was ejected through tangential openings at the end of pipes.

Source
A jet engine works the same way, throwing air overboard, in large quantity and at very high velocity. Compared to the boat experiment, we have replaced:

The stone by air. As air is much less dense than rock we need to concentrate a lot of air to get the same effects.

Hand muscles by fuel combustion. Combustion delivers high velocity gases by effect of gas expansion at hot temperature. The more fuel, the higher the gases velocity.

Burning a lot of fuel requires a lot of air, we have already a need of air in large quantity, so this is not a problem. However air won't come in large quantity into the engine, at some point air already present in the engine prevents more air to enter. In flight, ram air pressure can increase the quantity of air in the engine, but this isn't enough.
The solution is to use a compressor to fight the pressure of air already in the engine, and push, on large airplanes, about one ton of air per second in it. It's only 50 times more than our stone, but the exhaust velocity is definitely not the same: About 1,000 km/h.
How do we collect a lot of air, and eject it at high velocity?
We have all the ingredients to make a jet engine, which is composed of three sections (to simplify, let's look at an early turbojet engine, refer to this question for common turbofan):

Air enters in the engine from forward and is compressed by a pump (named the compressor) to increase the quantity available.

Compressed air is mixed with fuel and lit. Air is required for fuel to burn (oxygen). During the combustion, the mix achieves a very high temperature and expands under the effect of heat, exactly like water vapor expands in a pressure cooker or an aeolipile.

Before being ejected as small part of the hot gases energy is used to turn a turbine (like wind turns a wind turbine). This rotating motion is transferred to the compressor we saw at the beginning. To start the compressor at the beginning a starter is used, like on a car.

Hot gases are ejected rearwards this creates the forwards reaction of the engine.

The components of a jet engine are therefore:

A compressor to force air into the engine.
A combustion chamber to create rapidly expanding gases from air and fuel.
A turbine to turn the compressor.
An exhaust to release the gases in an optimized way to increase efficiency.

Source

I can't believe I've never seen this answer before, but +1 for the man in the boat!

There are three basic parts to a gas turbine, a compressor, a combustion chamber and a turbine. Air is compressed by the compressor, heated by the combustion chamber and the heated air powers the turbine. The turbine in turn powers the compressor.
The key is that the heating in the combustion chamber causes the air to expand. This means that the work that can be done by gasses (air plus combustion products) exiting the pressurised combustion chamber is greater than the work needed to force the incoming air (and fuel) into the combustion chamber.
The available energy in the exhaust can be used in various ways. The simplest is the turbojet, the stream of hot gasses coming out the back of the engine directly provides forward propulsion.
Alternatively we can capture more of the energy from the exhaust with a turbine and use it to drive a fan resulting in a turbofan.
Or we can design our turbine to capture most of the usable energy in the exhaust and direct it to a shaft which can be used to power all sorts of things.

A jet engine is an overcomplicated ramjet with extra turbines to let it work at lower speeds.
A ram jet works by igniting compressed incoming by mixing it with fuel and providing a spark.

hmmm... a ramjet lacks (moving) compressor stages, which are an essential component of a jet engine, and there is no bypass component and most of the time no supersonic flow. So perhaps more distant relatives than siblings?

@yankeekilo that's why I said overcomplicated :)

LOL, but then a barrel of fuel and some matches may also claim commen ancestry :D

A ramjet is almost totally different from a turbojet (and its derivatives). It lacks a fan/compressor and a turbine, so it would only confuse people to compare them. Once you have a turbojet down, you can look at pulsejets, ramjets, scramjets, and other more esoteric forms.

I don't see why you say it's "overcomplicated" -- it seems that a jet engine is exactly as complicated as it needs to be for its intended operating environment.


text:
What is the name of this aircraft?
The photo was taken in Daegu, South Korea and is not visible on Flightradar24. I could hear the sound of turboprop engines.

(full image)

My first thought was King Air C90 but the image quality is too poor to be sure.

I'd guess Piper Seneca. I know it's not a turboprop but that looks like it.

Perhaps it's a CASA/IPTN CN-235? It meets the turbo-prop criteria, and the wing looks similar. South Korea operates the type

The Seneca has a constant chord wing where this aircraft has a taper. The CN-235 is a high-wing design while this aircraft is clearly low wing.

I too think it might be an early King Air 90. Or maybe an RC aircraft. https://hobbyking.com/en_us/avios-pnf-kingtwin-1700-sports-scale-executive-turboprop-airplane-1700mm.html

Do you have any other images or perhaps a video link we could use to help identify the aircraft?


text:
What is this object that is transported onboard an ambulance aircraft in Sweden?
While watching the news on 7 November, I saw this picture:

The news clip (playhead position 18:29) is talking about an ambulance or organ-transportation aircraft in Sweden, which tail-id is SE-RVA.
What is this coffin-shaped object with monitors and windows, that is transported in the picture and what is its purpose?
It seems the object is transferred from the aircraft to an ambulance using the metal support with wheels that can be seen to the left in the picture.

This question is not about aviation and is rather about a specific piece of cargo. Maybe go to Medical Sciences Stack Exchange.

Not an aviation question. It would have been just as meaningful to ask about the metal box being placed on an ambulance. And just as off topic.

I don’t agree that this is off topic since this is probably an object especially designed for air transport (even though I have no idea what it is).

@mins The key is that it meets RTCA DO-160.

It's an incubator for newborn infants designed for air transport. In particular, it's an International Biomedical NxtGen.

(Manufacturer's promotional photo)


text:
What is the reason for a taxiway centerline to extend parallel to the runway centerline?
Why does the taxiway centerline extend on this long distance on the runway?

It’s not leading to the runway. It’s leading off the runway. It indicates where nose of the plane should be in order turn to get off the runway and not hit anything on the way off. You will also see the yellow lines crossing the runway where a taxiway crosses a runway.

On a long runway (see below), for a taxiway used as an exit, the lead-off starts 200ft before the tangency point. This corresponds to the length of a stripe (120ft) and a gap (80ft).
This lead-on is important for low-visibility operations to make the pilot aware of the proximity of the curved segment. A random taxiway lead-off at KSFO:

(This place on Google Maps)
ICAO recommends this distance in Annex 14 of the Chicago Convention: 30m (100ft) or 60m (200ft):

5.2.8.7 Recommendation.— At an intersection of a taxiway with a runway where the taxiway serves as an exit [...] The taxiway centre line marking should be extended parallel to the runway centre line marking for a distance of at least 60 m beyond the point of tangency where the code number is 3 or 4, and for a distance of at least 30 m where the code number is 1 or 2.

(Code 1 runways are less than 800 meters long, Code 2 runways are 800-1199 meters long, Code 3 runways are 1200-1799 meters long and Code 4 runways are 1800 meters or more in length.)
This ICAO recommendation is usually implemented by State members, for the US/FAA in FAA Standards for Airport Markings, AC 150/5340-1 at §4.2.3.2.1. E.g. for the case of a taxiway joining the runway at an intermediary location:

For taxiways that intersect a runway at any other locations than at the runway end, as shown in Figure A-16, the taxiway centerline marking
curves onto the runway and extends parallel to the runway centerline marking for a distance of 200 feet (61 m) beyond the point of tangency
with the runway centerline [...]


text:
Shouldn't the crew of Helios 522 have felt in their ears that pressure is changing too rapidly?
Since Helios 522 was unpressurized all the time, shouldn't the faster-than-usual change of interior air pressure during the ascent have alarmed the pilots that something isn't alright because their ears would feel a more rapid change of pressure, possibly hurting because of the faster change? Within 15,000 ft the TUC is unlimited so they should have become suspicious that their ears hurt that much and be able to do something about it if they realized the danger, shouldn't they?

Airliners don't climb fast enough to cause a dramatic change in pressure that would be immediately noticeable.  And besides, ears don't "hurt" going up...

@MichaelHall Now that you say it, indeed I remember that when my ears hurt it was during a plane's descent rather than ascent. Unless perhaps when I was sick, but it's a long time, I don't recall well. So ears only hurt when the exterior pressure gets higher than the one within the Eustachian tube?

As a general rule, without going into specifics of this particular case, no.
One does not necessarily notice, or rather pay attention to pressure changes if you fly a lot, which is the case of professional pilots. Equalizing the pressure inside the ears becomes pretty much a reflex that goes unnoticed.
In the case of passenger planes (and military jets even more so) the rate of ascent is relatively high, which sneaks the lack of oxygen into the equation. One does not need to climb very long for the effect of thinning air to accumulate, numbing the senses and compromising the judgement.

I thought it is because they fly a lot that they would notice a more rapid change than usual.

@Giovanni If the outflow valve wasn't fully open, it might moderate the (cabin) rate of climb somewhat, enough to make the higher rate less obvious. Years ago, I had an unpressurized maintenance ferry flight, although with both packs working (as they were on the Helios flight). At 10,000', the cabin wasn't all the way there, and I had to hold the outflow valve control to OPEN much longer than I'd normally do (this was when we did cycle it manually during preflight checks) to get a 10,000' cabin. So it may have been less than fully open, enough to shallow but not stop the cabin's rate of climb.


text:
What were the atmospheric models in the 19th century and early 20th century like, compared to the present-day ISA?
Atmospheric pressure has been used to determine the altitude a pilot (or a mountain climber as well) is at since the beginning of the age of ballooning.
I find the following Wikipedia excerpt about Green's and Rush's ascent interesting: "[...]they reached the elevation of 27,146 feet (8,274 m), or about five miles (8 km) and a quarter, as indicated by the barometer, which fell from 30.50 to 11". (emphasis mine)
11 inHg is 5.403 psi or 0.3725 bar. Today, this corresponds to an altitude of 25300 ft (7.7 km) in the ISA and therefore that's the altitude that would be shown by today's plane's altimeter at Green's and Rush's altitude, i.e. today they would be considered flying quite lower than by the 19th century's standard.
So I wonder how the established atmospheric model in the 19th century differed from the ISA within 36,000 ft (11 km) of altitude. And what pressure was considered the sea level datum? When was the 29.92 inHg (14.696 psi) sea level used for the first time?
At the beginning of the 20th century the stratosphere was discovered with radiosondes going up to 17 km (56,000 ft) and I wonder how the model changed then, e.g. what pressure altitude model(s) were used by Gray's and Piccard's barographs? In August 1932, together with Max Cosyns, Piccard reached an absolute altitude of 16.9 km but a barometric altitude of 16.2 km. That's an example of where I wonder how their barograph differed from present-day altimeters in terms of pressure.

I think there's a possibility that the altitude is given with too much precision - the article doesn't state the resolution of the barometer reading, which might only have been 0.25" or even 0.5".  A lesson that Wikipedia itself should not be trusted, only the references it cites, perhaps?

@Tevildo Even 10.5 inHg would be 5.16 psi which today would still be a considerably lower altitude than 27146 ft where pressure is less than 5 psi.

True.  The figure of 27,146 feet is in the source document (the first edition of the DNB), which cites a number of nineteenth-century publications, but without specifying which one they use for this particular fact.  We know it's the result of a contemporary calculation, at least, not an artifact of Wikipedia.

@Tevildo and Giovanni – I haven't commented on differences in precision in my answer below, but I think there's a compelling answer that the understanding of atmospheric physics was sufficiently different to change the pressure/height relationship fairly substantially. That said, the fact that it's approximately an exponential means that small errors in measurement are important, which would be an additional source of error beyond that in the atmospheric model used.

This is a fascinating question and its answer would arguably be better suited to a rather longer article than a Stack Overflow post: you're effectively asking (1) what is the history of the development of the ICAO standard atmosphere model, and (2) what version of it therefore was used -- and therefore (3) what is different now compared to then to explain the discrepancy.
Briefly, the answers to these are (1) – very complicated (2) – complicated and (3) an improved understanding of the tropopause and a better quantification of features of the atmosphere such the dry adiabatic lapse rate (which I think wouldn't have been used in the 19th century, but would have been in the 20th).
(Just as a reminder, the difference in the tropopause matters, because, in modern notation, atmospheric pressure varies with height as $\frac{dP}{dh}=-\rho g$ and the ideal gas law in molar form gives us $P=\rho R T(h)$ -- so you need to know solve both simultaneously in order to work out height from pressure).
It transpires that it is important to keep in mind that the flights you mention occurred in 1838 in Britain (by Green and Rush – who were British) and in 1932 in Switzerland (by Cosyns and Picard – who were Belgian and US citizens respectively).
Probably the best reference to the early history I can easily find is this review from 1977 [1] to put the then-new 1976 Standard Atmosphere in context. Quoting from it extensively to answer the developments in the 20th century first (I shall return later to the 19th):

[...] Aneroid barometers were calibrated [...] in accordance with an isothermal standard atmosphere. A British standard
atmosphere of this era [Airy, 1867] provided a table of aneroid
pressures as a function of height from 0 to 3657.6 m (12,000
feet) computed on the assumptions of a sea level pressure of
31.0 in. (787.4 mm) of mercury and a constant mean temperature of 50 ºF (10ºC)
[...] This model was used as the basis of barometric altimetry in the US until after World War 1. During the early part of the twentieth century the French had a different standard atmosphere for height determination, based upon a nonlinear temperature-height function proposed by Radau [1901]. According to Grimault [1920] the French aeronautical community until 1920 depended upon this 'Law
of Radau' as the temperature-height function in a standard
atmosphere used for normalizing measurements of aircraft
performance.

This didn't quite work, however, as the $P, T$ relationship deviated substantially from reality as measured at altitudes above 5 km, and after 1920 atmospheric sounding (balloon) measurements were taken up to heights of around 14 km. This discrepancy, between physics and reality, was highlighted by an Italian military engineer, Gamba, when he published a graph of the ten-year averaged data of temperature vs height in the range of $(0, 20)$ km in the Pavie region of Italy. These measurements lead to a piecewise linear adjustment to the model:

Using Gamba's curve as a basis for comparison, Toussaint [1919] noted the limitations of the Radau temperature-height expression and showed the close agreement between Gamba's observations and a two-segment linear temperature-height function consisting of a constant negative gradient, -0.0065 ºC/m from +15ºC at sea level to -56.6 ºC at 11,000-m altitude, and a zero gradient from 11,000- to 20,000-m altitude.

It appears that this model had some apparent success and was closer to reality -- at least, as far as early aviators and metrologists could tell. Naturally, the US decided to do its own thing.

Toussaint computed tables of atmospheric pressure, temperature, and density as a function of altitude in increments of 500 m from 0 to 11,000 km and in increments of 1000 m from 10,000 to 20,000 m. This proposal led the French [Grimault, 1920], in April 1920, to adopt the Toussaint temperature model as the basis of a new aeronautical standard atmosphere. Grimault, noting that the available meteorological data (primarily for western Europe) generally supported the Toussaint model, emphasized the advantages to be gained if cooperating European countries would each adopt the same standard. Italy and England soon followed this advice [British Aeronautical Research Committee, 1922], while the United States,apparently intending to do likewise,adopted only a portion of that model, a situation which led to confusion shortly thereafter and to some disagreement many years later.

Why? Well, in 1921 the US executive committee of the National Advisory Committee for Aeronautics (NACA) met, and they adopted for performance testing Toussaint's formula linking temperature, pressure and height.

This statement, with no height boundaries and no mention of an
isothermal region,appears in Gregg's document,which limited the listing of computed atmospheric properties to heights between 0 and 10,000 m while showing observed properties for a much greater height range. This document implicitly limited the maximum height of the 1922 U.S.Standard Atmosphere to about 10,000 m (33,000 feet).

What happens next is fairly typical: Europe develop Toussaint's formulae and model in one direction, and the US in another, and a discrepancy arises. The details of this happen to correspond exactly in time to the period you ask about:

The growing requirements for standard atmosphere tables by the aeronautical community as well as by artillerists led Diem [1925] to expand the U.S. Standard Atmosphere. This expansion included the following points: (1) increasing the height resolution; (2) adding listings of ratios of the several properties to their sea level values; and (3) extending the altitude range from a maximum of 10,000 m up to 20,000 m (but in a manner not consistent with the Toussaint
model in the ICAN standard) [emphasis mine]

Diehl, like Gregg, appears to have been unacquainted with
the complete Toussaint model as well as with the actions of
ICAN, for while he properly extended the range of the constant lapse rate of temperature (-0.0065ºC/m used by Gregg) to heights above 10,000 m, he unfortunately extended it only to a height of 10,769 m (see $G D_1$ in Figure 1), where the computed temperature becomes -55ºC (in accordance with Gregg's mean of observed temperatures for 45ºN in the United States). Then from 10,769 m to 20,000 m altitude, Diehl introduced an isothermal layer at -55ºC (see $D_1 D_2$ in Figure 1) instead of the one previously adopted at -56.5ºC in the Toussaint-ICAN standard ($T_1 T_2$ in Figure 1). The slight difference in the height and temperature of the tropopause (231 m and 1.5ºC, respectively) later led to international aeronautical confusion which was not resolved until after World War II. [emphasis mine]
In the interim it was decided that in the United States, in accordance with the actions of ICAN, altimetry would no longer be based upon an atmosphere isothermal at 10ºC [National Bureau of Standards, 1920] but rather would be based on the same standard used for comparison of aircraft performance. The metric altimetry tables of ICAN, however, were neither in agreement with the U.S. Standard Atmosphere [DieM, 1925] at heights above 10,769 m nor convenient in the United States, where measurements were made primarily in English units. Furthermore, Diehl's English tables of pressure versus height
were not conveniently formulated for altimeter calibration. Consequently, Brombacher [1925, 1935], of the U.S. Bureau of Standards, prepared tables of altitude as a function of pressure as well as other tables particularly applicable to the calibration
of altimeters.

I therefore propose that it is likely that some variant of the Toussaint model, either in the convenient pressure or temperature table -- due to Brombacher in 1925 (available online [2]), or the slightly different European version codified by the predecessor to ICAO, ICAN [3]  -- to have been that used for the 1933 flight. Exactly which version probably needs detailed historical investigation to determine: it depends on the detail of their equipment's manufacturer and I can't find a good amount of info on that online, but I think it's going to be the US one (Brombacher 1925) as (i) Picard was a US citizen (ii) the use of that model results in a larger discrepancy and possibly a larger height, and (iii) most certainly it would have been convenient to use at the time as the actual publication provides a look-up table of height vs pressure. It's quite clear, however, that the difference between our "modern" ICAO atmosphere and measurements at that time largely coming from the understanding of the tropopause (set in 1976 as being 11 km geopotential altitude and at -56.6 ºC – very close to Toussaint's model) – I haven't (yet) done a detailed calculation to see if it explains all of it mathematically, but one could. Edit - it transpires it's a bit hard to recreate Toussaint's original publication because I don't have access to it, and I wouldn't understand physics in French if I did (physics in english is fine ;-) ). However, as a rough demonstration of the size of the effect this gives, here's a plot of a very hacky numerical solution to the two different atmospheres as a function of height, up to the stratosphere – although the tropopause is at 11 km, they're quite different before that:

These discrepancies in atmospheric models were slowly, slowly ironed out over much of the next 30 to 50 years (spurred on, I suspect, by increased aviation co-operation during WW2), and the final standard atmospheric models we have today contain detailed information well outside of the Kármán line, as is required by spaceflight operations.

The situation for the Victorian aero-naught is rather different, and I have to say, harder to pin down. At present, I can't easily access the original works of Mr Airy, The Astronomer Royal on determination of heights from barometer readings, Proc. Roy. Meteorol. Soc., 3, 407-408, 1867, which I suspect contains a pressure-height curve in detail (not least as Fig 1 above indicates that it is isothermal), but I am aware that the knowledge of physics behind this is far older: the relationships between pressure, volume and temperature are largely 17th century in discovery and 19th century in detail (the ideal gas law was written down in one unified form in 1834 by Claperyon). M. De Luc writes in the Philosophical Transactions of the Royal Society in 1774 a detailed account of solving this problem with the most wonderful title [4]:
M. De Luc's Rule for Measuring Heights by the Barometer, Reduced to the English Measure of Length, and Adapted to Fahrenheit's Thermometer, and Other Scales of Heat, and Reduced to a More Convenient Expression. By the Astronomer Royal.
To cut quite a lot of the 13 pages of Georgian verbage and vital experimental detail and notes such as the differences between French and English feet (!!!), he espouses, entirely in the third person:

[...he] thus corrected the height of both of his barometers (that at the bottom, and that at the top of the hill) for the particular degree of heat, indicated by a thermometer attached to the barometer [... and] calling the two altitudes of the barometer $B$ and $b$, and putting $\log B$ for the logarithm of $B$ [...] and calling the heights of this [carefully calibrated] thermometer at the two stations be called $G$ and $I$ [...]
[...] the formula that will give the height of the upper station above the lower one, in English fathoms will be $$\log B - \log b \mp d \times I + \frac{G+I}{1000}$$.

I think it is possible to probable that approaches of this sort were used by Green and Rush; an 1863 publication (again in Phil Trans) entitled "On a Simple Formula and Practical Rule for calculating Heights barometrically without Logarithms" [5] does much the same thing using a more complicated linear approximation that involves a cosine of latitude, lookup tables and, frankly, is equally awful (to the modern eye). All of these were interested in assessing elevation rather than altitude per se -- in other words, how tall is that mountain, rather than how high is my balloon, but I am somewhat convinced that the basic physics would have been understood at the time, because the earliest balloon flights used a barometer as an altimeter (the first recorded use is, I think, in the Charliére, the successor to the Montgolfiére, in December rather than September 1783 [6]), presumably with an isothermal atmosphere. However, I can't answer this more concretely and it is difficult to know exactly what model would have been used at the time – if evidence emerges, I reserve the right to edit this in the future.
An obligatory, relevant XKCD to end with:

References
[1] Minzner, R. A. (1977). The 1976 Standard Atmosphere and its relationship to earlier standards. Reviews of Geophysics, 15(3), 375. https://dx.doi.org/10.1029/rg015i003p00375
[2] Brombacher, W. G. (1925). Tables for calibrating altimeters and computing altitudes based on the standard atmosphere. https://ntrs.nasa.gov/citations/19930091313
[3] International Commission for Air Navigation, Official Bulletin,vol. 9, p. 27, resolut. 226, Montreal, 1922. https://books.google.dk/books/about/Bulletin_Officiel.html?id=CAngAAAAMAAJ&redir_esc=y
[4] De Luc, M. (1774). M. De Luc's Rule for Measuring Heights by the Barometer, Reduced to the English Measure of Length, and Adapted to Fahrenheit's Thermometer, and Other Scales of Heat, and Reduced to a More Convenient Expression. By the Astronomer Royal. https://archive.org/details/philtrans01544508/page/n11/mode/2up
[5] Ellis, A J. (1863). On a Simple Formula and Practical Rule for calculating Heights barometrically without Logarithms. https://dx.doi.org/10.1098/rspl.1862.0107
[6] Gibbs-Smith, C. H. (2010). Notes on the History of Ballooning. https://www.cambridge.org/core/journals/journal-of-navigation/article/abs/inotes-on-the-history-of-ballooning/5FD910C7F47D61FE80FD16D4CC7BC9F8

What a wonderful answer! Thank you!

Thank you, very interesting all that. But I think Piccard used the European Toussaint model because he was a Swiss (not an American citizen at that time I think, whatever he was a Swiss) and for the first time ascended with German Paul Kipfer, and the 2nd time with Belgian Max Cosyns (and both times from Europe) so they near-certainly used the European model. However, Hawthorne C. Gray in 1927 must have used the U.S. model with the isothermal layer beginning at 35,300 ft.

@Giovanni Fair enough! My mistake – I didn't realise that and hadn't done enough reading around the subject; the US discrepancy was further from "the truth" and I naïvely assumed it would lead to the fairly large deviation reported.

Thank you. I had to smile at "as is required for spaceflight operations" because at their time Jeannette Piccard was (and sometimes still is, even by Valentina Tereshkova in some way) considered the first woman in space. She and her husband Jean reached 57,500 ft (17.5 km) in 1934. The Piccards seem to have had a definition of being in space as at the altitudes where you must wear a pressure suit, i.e. above 50K ft (15 km) or at a pressure lower than 1.7 psi (~ 0.12 bar).

To assist any researchers - the main sources used by the DNB and hence by Wikipedia are "Aeronautica" (1838) by Thomas Monck Mason and "Astra Castra" (1865) by Hatton Turnor.  Neither have the 27,146' figure for Green's flight, but they do have an even more precise figure of 22,977' 4" for Gay-Lussac's flight of 15 September 1804.  The formula which Gay-Lussac used to calculate his altitude is the probably the one to look for.


text:
How is a stall different from a spin?
Is a spin a by-product of a stall? So if a airplane stalls is a spin guaranted sooner or later?

If you are in a spin your wings are stalled but not all stalls are spins.
This description puts it pretty nicely:

If a stalled aircraft is subjected to a sufficient yaw rate, it will
enter a spin. The yaw can be induced by improper use of the rudder or
can be a result of the wing drop characteristics of the aircraft in
question. In a spin, both wings are in a stalled condition but one
wing will be in a deeper stall than the other

You can keep an aircraft stalled without spinning it, and the spin will only occur when some kind of yaw aggravation induces it. But to dig into that statement a bit there are two things to note "improper use of the rudder" and "wing drop characteristics" these things can be common in lots of scenarios which is why stalls are a maneuver to be done with caution and at least one eye on the ball at all times. Spins are not "guaranteed" as long as you are in proper control of the yaw axis.
If you want some examples, scenarios like that which AF447 encountered lead to a stall that did not become a spin. More benign, all student pilots are taught stalls and stall recover generally fairly early on in training, broadly these dont lead to spins or at least should not if the instructor is paying attention.

A stalled airplane is moving straight ahead and the airflow disruption is more or less the same on both wings, mostly separated but with some attached flow near the tips giving aileron control and still providing some lift and driving the plane forward somewhat, in a straight line.
If you hold back one of the stalled wings and make the airplane yaw, the held back wing's AOA rises, so it stalls more and becomes a sort of anchor, and the opposite wing moves ahead, so its AOA decreases and partially un-stalls a bit more.
The unstalled part of the wing is still making lift and the lift vector is producing a thrust component that drives it forward, as when gliding straight, so, the thrust being on one side only, the autorotation starts.
One wing is trying to glide forward, but the other wing is kind of stuck in the mud, so the gliding wing circles around the stuck one.
The center of rotation in a spin is generally around 1/3rd span on the fully stalled wing, so the inside tip might actually be moving backwards a bit.

You can think of a spin as a special case of a stall, in which one of the wings is mostly stalled and the other is mostly not stalled. the wing that is still mostly flying and generating lift rolls the airplane up on its side and points the nonflying wing down and the plane then swings nose-down and begins rotating around the roll axis with its nose pointing steeply towards the ground.
This means it is a common occurrence to enter a spin right after experiencing a stall if one wing resumes flying before the other does.
Since the plane's propeller is swirling the air around the fuselage and wings in one direction, the propwash encounters one wing from below and the other wing from above. This results in a plane that "wants" to spin more easily in one direction than the other, and can be brought out of a spin more easily in one direction than the other.
So... a spin starts with a stall that then develops asymmetrically. Depending on the design of the plane, it may be possible to control the plane through a stall so a spin does not develop during the stall break or the stall recovery. In other planes it takes skill to avoid a stall-spin event and even greater skill to successfully recover from one.


text:
What is the outer kink on the airbus 340-600?
I was checking some information about the a340-600 and got this statement: "thickness/ chord ratios 15.25 per cent at root, 11.27 per cent at inner kink, 9.86 per cent at outer kink and 10.60 per cent at tip"
I know where the inner kink is but what is the outer kink and where is it located?

I edited a few things to make your question a little more readable.  If I deleted anything important, feel free or roll back the changes.  Welcome to Aviation.SE!

The outer kink on A340-600 wing is located just outboard of the outboard engine, note trailing edge kink in planform drawing.

it is not that visible at first glance

@IbrahimJaafar Indeed not, but a straightedge helps ;)